The present application claims the benefit of Finnish application No. 20000800, filed Apr. 5, 2000 and Finnish application No. 20002330, filed Oct. 24, 2000.
The invention relates to a radial tire for vehicles comprising: Viewed in order, starting from the outer surface in road contact towards the inner parts of the radial tire: a tread in road contact, the tread comprising a surface that is in road contact while the tire is in free rotation and two shoulder areas on both sides of the central plane of the radial tire: an undertread having principally the same width as the tread, one or more belt layers having principally the same width as the tread, and one or more plies, which extend from the first bead area to the second bead area of the radial tire, the opposite side of the belt layers of the plies forming the inner surface of the radial tire together with the inner liner; In the following order, on both sides of the tread symmetrically with the central plane of the radial tire: two tread wing areas extending the shoulder area, two sidewalls, and two bead areas.
Cross-ply tires have been increasingly replaced with radial tires in vehicles, especially in construction machines, jeeps, police cars, ambulances etc., because the benefits achieved with radial tires are, for instance, improved traction power and lower fuel consumption. In addition, when used in construction machines, radial tires leave shallower grooves in the terrain. Nevertheless, during use, the tires of jeeps, construction machines and the like frequently hit sharp stones, stubs, branches and similar, and then especially the tire sides are exposed to damage. This involves a greater problem with radial tires than with cross-ply tires, because the rigid belt layers of radial tires support the tread of the tire, so that the tire is more flexible at its sidewalls under load.
There have been attempts to solve this problem in the way described in U.S. Pat. No. 5,078,192, for instance. This publication describes a shield against side cuts made of a ply that consists of aligned and parallel filaments. This side-cut shield is disposed on the sidewall of the tire, and it does not extend to the area under the tread of the tire. However, such a design may entail the problem of the joint between the side-cut shield and the tread being weaker than the surrounding area.
JP patent specification 4, 163, 209, in turn, describes a side-cut shield extending from one bead area of the tire to the other, i.e. over the entire tread. Such a design would not be usable in a radial tire, because it would stiffen the tire structure and thereby eliminate the benefits of radial tires compared to cross-ply tires.
Thus the object of the invention is to provide a side-cut shield in a radial tire for vehicles, which is efficient against sharp cuts, easy and straightforward to manufacture, and yet does not impair the good properties of radial tires.
These objects have now been achieved in the way described in the accompanying claims.
The invention relates to a radial tire, which is characterized by the fact that it comprises two side-cut shields disposed on both sidewalls of the radial tire, the side-cut shields comprising at least two ply layers, the plies comprising a first filament array consisting of mutually substantially parallel filaments, and a second filament array consisting of mutually substantially parallel filaments, the filaments in the first filament array being disposed at an angle xcex1 relative to the filaments in the second filament array, the angle xcex1 being in the range 20-90xc2x0, and the side-cut shields being disposed so as to extend from the bead areas of the radial tire to the shoulder areas of the radial tire, with the edges of the side-cut shields facing the shoulder area disposed between the belt layers and the plies.
Consequently, the web-like side-cut shield of the invention provides efficient protection for the tire sides especially against sharp cutting loads, such as branches, stubs and stones. At the same time, they provide an enhanced shape of the sides of the radial tire, which are more upright than those of conventional tires, allowing the tire sides to avoid obstacles easier. In addition, the side-cut shields of the invention stiffen the tire sides and thus stabilise the behaviour of the tire during running by reducing swaying of the tire. The radial tires of the invention thus allow good protection to be obtained for the tire sides against cutting loads, in accordance with the objects of the invention. In addition, the side-cut shields of the invention do not have any impairing effect on the properties of the radial tire, but on the contrary, further enhance the benefits of radial tires over cross-ply tires.
In accordance with the invention, the filaments in the filament arrays run at an angle of 20-90xc2x0 relative to each other. With a smaller angle xcex1 between the filaments, as in U.S. Pat. No. 5,078,192, where it is 0xc2x0, the side-cut shield provides notably poorer protection against cutting loads than with an angle within the range 20-90xc2x0 as mentioned above.
In one embodiment of the invention, the angle xcex1 between the first and second filament array is 30-70xc2x0, preferably 40-60xc2x0. Similarly, there may be a desired number of ply layers, such as 2-10 layers. However, the preferred number of layers is from two to four, depending on the purpose of use of the tire. If there is a plurality of plies, they are preferably overlapping.
In a preferred embodiment of the invention, the filaments in the filament arrays are made of an organic or inorganic material, such as steel, polyamide, aromatic polyamide or rayon. Yet it is obvious to those skilled in the art that the material of the filaments, the number of plies and the angle between the filament arrays can be freely selected within the scope of protection of the invention in order to achieve the desired result.
In a further preferred embodiment of the invention, the side-cut shields are disposed symmetrically on both sides of the central plane of the radial tire. In this context, the central plane implies the plane that is perpendicular to the axial line and runs transversely to the radial tire through the centre of the tread width.
The sidewalls of the radial tire of the invention may comprise, viewed from the outer surface towards the inner parts of the radial tire, e.g. a sidewall, possibly ply turn-ups, plies and an inner liner. Accordingly, the bead areas of the radial tire of the invention may comprise, viewed from the outer surface towards the inner parts of the radial tire, a clinch, possibly ply turn-ups, an apex and a bead wire, plies and an inner liner. In addition, the bead area comprises an ankle, a heel, a bead base and a toe. It is obvious to those skilled in the art that the side-cut shields of the invention are applicable also to tires with a different design.
In one embodiment of the invention, the side-cut shields have been disposed on the sidewalls between the sidewall or the clinch and any ply turn-up provided or the plies.
In a preferred embodiment of the invention, the side-cut shields may extend to the shoulder areas, starting from their edge facing the wing areas to a distance accounting for 5-100%, preferably 25-95% of the width W of the shoulder area. When the side-cut shield extends to the shoulder areas of the radial tire, preferably underneath the belt layers, optimal resistance against cutting loads is achieved in the entire tire. Also, the joint thus achieved does not form any critical point of discontinuity in the tire, as the materials join without any sharp joint.
In the bead area, in turn, the side-cut shields can be extended substantially to the heel areas, bead bases or toes of the radial tire. The side-cut shield can also be extended to the inner surface of the radial tire, e.g. to a height of the inner surface of the radial tire that accounts for 3-80%, preferably 5-30% of the lateral height H of the radial tire, starting from the toe. Then the side-cut shield extends through the bead base to the shoulder areas, preferably around the bead wire.
In the bead areas of the radial tire, the side-cut shields may be disposed
between the clinch an any ply turn-up provided or the bead wire in the heel, bead base and toe areas, and
between the inner liner and the plies in the areas of the inner surface of the radial tire.
The invention also relates to a method for manufacturing a radial tire for vehicles, comprising:
manufacturing a blank on a manufacturing drum by disposing on the manufacturing drum in the following order: among other things, plies extending from the first bead area to the second bead area of the radial tire to be manufactured, two sidewalls on both sides of the central plane of the radial tire to be manufactured and two shoulder areas on both sides of said central plane, the shoulder areas being disposed in the finished tire between the surface in road contact and said sidewall during free rotation of the tire,
disposing on the blank a belt package comprising belt layers and the undertread and having a width substantially equal to the tread of the finished radial tire,
disposing the tread on the belt package, resulting in the tire blank,
vulcanising the tire blank,
and the method is characterized by comprising additionally, between the step of disposing the plies and the sidewalls in the blank manufacture, a step of disposing on both the sidewalls of the radial tire two side-cut shields, which comprise at least two ply layers, which comprise a first filament array, which consists of mutually substantially parallel filaments, and a second filament array, which consists of mutually substantially parallel filaments, the filaments in the first filament array being at an angle xcex1 relative to the filaments of the second filament array, the angle xcex1 being 20-90xc2x0, and the side-cut shields being disposed to extend from the bead areas of the radial tire to the shoulder areas of the radial tire such that the edges of the side-cut shields facing the shoulder area are disposed between the belt layers and the plies.
The radial tires of the invention can obviously be manufactured by some other method. However, the method described above is one of the basic methods for manufacturing radial tires of vehicles, in which the fitting of side-cut shields has been included as a production step. Hence the method of the invention is easy and economical, it does not require auxiliary equipment or new working methods, since the side-cut shields are assembled in the tire in the same way as the other fabric layers. Moreover, the tires can be vulcanised in the same mould regardless of the fact whether the tire blank includes side-cut shields or not.